Seed viability loss at low temperature genebank and ambient storage received increasing concerns, but comparing with its importance, few publications dressed this question. In this paper, viability monitoring data of wheat (Triticum aestivum Linn.) seed from a midterm genebank, ambient storage, as well as an accelerated ageing experiment were quantified to get further understanding of seed ageing under these conditions. The results showed that seed longevity of all accessions followed normal distribution, and that seed survival curves showed inverse-S shape, which received no obvious effects from storage conditions. The rate of seed viability loss decreased, and the plateau phase and seed longevity increased as the storage temperature reduced. T-test was adapted to determine the turning point (Pt) between the plateau phase and viability sharp decline phase of the seed survival curve. The results showed that the Pt under different storage conditions were quite close, which varied between 82.2% and 83.6%. The possible role of Pt and some physiological indexes as indicators for seed viability loss during germplasm storage were discussed.